New Tekonsha Prodigy.Old Trailer
If the trailer brakes worked before, and all that was done was to switch controllers in the tow vehicle then there is likely a corrossion problem in either the car or trailer end of the umbilical cord.
When I picked up my '64 Overlander at Ace Fogdall RV Saturday after its round of Winter Maintenance, all trailer features operated except the trailer brakes. As it turned out the terminal for the trailer brakes on the tow vehicle end of the umbilical cord arrangment had nearly disintegrated due to corrossion. A quick replacement with a new Pollack connector and the trailer was back on the road again. Had a similar problem with my '78 Argosy and its problem was with corrosion on the trailer end terminal - - it also required a new connector to get all functioning properly again.
All that is required to examine the terminals on your connectors is a fine "jewler's" style screw driver to remove the set screw - - depending upon how long it has been since it was last removed it might be a good idea to soak the set screw with penetrating oil. It would pay to be preapred with a new car and trailer end for your connectors so if a replacement is needed it can all be handled at once - - a wire cutting/stripping tool comes in handy for this process as well as a roll of heavy duty electrical tape to warp the connector before re-installation.
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)